Looking at data from 50 countries over the second half of the 20th century, the study found the majority of deaths in young people was through incidents such as car accidents or reckless behaviour. Violence and suicide have also become key causes of death in this group.

The strong international focus on reducing infant and child mortality has not been matched by a similar efforts in older groups.

"These trends are likely to continue because mortality in children younger than five years is expected to decline further, and injury-related mortality is expected to increase in the next 25 years," said Russell Viner.

Particularly toxic

Commenting on the findings, Michael Resnick, who was not involved in the study, said they showed how "the profound health and social changes that have accompanied economic development and urbanization are particularly toxic for young people in both high-income and low-income settings."

A study in 2009 by World Health Organization-supported researchers found that 40% of adolescent deaths were due to injuries and violence.

Viner's team used the WHO mortality database to analyse data for 50 rich and poor nations between 1955 and 2004. They looked at patterns of mortality by age group, sex and cause of death - divided into infectious diseases, chronic diseases and injury.

Findings showed that in the 1950s, mortality in the 1 to 4 age group far exceeded that of all other age groups in all regions studied. But in the 50 years up to 2004, death rates in children aged 1 to 9 fell by 80 to 93%, mostly due to reductions in deaths from infectious disease.

In contrast, declines in death rates in those aged 15 to 24 years were only about half that in children, largely because of increases in injury-related deaths, particularly in young men.

The researchers found that by the start of the 21st century, injuries such as in incidents like car crashes and street or gang violence were responsible for 70 to 75% of all deaths in young men aged 10 to 24 in all the regions studied.

By 2004, suicide and violence were responsible for between a quarter and a third of deaths in young men aged 10 to 24 years, and death rates in young men aged 15 to 24 are now two to three times higher than in boys aged one to four, they said.

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